Conventionally, an inkjet printer which includes a head having a plurality of outlets and controls ejection of fine droplets of ink from each of the outlets while moving the head relatively to an object, to thereby record an image, has been used. In such inkjet printer, ejection of droplets is accomplished by input of an ejection pulse to a piezoelectric element provided in the neighborhood of each outlet of the head, for example. According to a method disclosed in Japanese Patent Application Laid-Open No. 10-81012, a driving signal output per printing cycle consists of four driving pulses of a first pulse, a second pulse, a third pulse, and a fourth pulse, and a diameter of a dot recorded on a recording paper is variably controlled by appropriately selecting one or some of the driving pulses, to thereby achieve multiple tone printing.
Also, according to a method disclosed in Japanese Patent Application Laid-Open No. 2005-212411, a gentle vibration signal which vibrates meniscus in a nozzle so gently that ejection of ink in channels from the nozzle can be avoided is continuously applied to all channels regardless of presence or absence of image data, and an ink ejection signal is generated by including therein the gentle vibration signal depending on image data, to thereby constantly record a high-quality image with high reliability.
Meanwhile, in recent years, there is a demand for high-speed recording of an image, so that a cycle for input of a driving signal to a head is becoming shorter. Along with this, limitations are put to a waveform of an ejection pulse which causes ejection of a droplet in a driving signal, and thus, in some cases, it is difficult to form a dot of a desired size by using only one ejection pulse. While there is an approach of using a combination of a plurality of ejection pulses to form a dot of a desired size, use of a plurality of ejection pulses in forming dots of respective sizes results in increase in the number of ejection pulses included in a driving signal. Accordingly, the driving signal becomes too long to cope with speed enhancement in image recording. As a result, the quality of an image is reduced.